Halogenated butyl rubber

ABSTRACT

An improved halogenated butyl rubber wherein the polymer has a conjugated diene content of less than 0.25 mole % and a halogen content of at least 0.6 wt. %; at least 20 mole % of the halogen being in a primary allylic configuration.

This is a division of application Ser. No. 597,187, filed 4-5-84, nowU.S. Pat. No. 4,632,963.

BACKGROUND OF THE INVENTION

One of the first olefinically unsaturated synthetic elastomers to becommercially produced was butyl rubber. The expression "butyl rubber" isused in the rubber industry to describe copolymers made from apolymerization reaction mixture having therein from 70 to 99.5% byweight of an isoolefin which has about 4 to 7 carbon atoms, e.g.isobutylene, and about 30 to 0.5% by weight of a conjugated multiolefinhaving from 4 to 14 carbon atoms, e.g. isoprene. The resultingcopolymers contain 85 to 99.5% by weight combined isoolefin and about0.5 to about 15% combined multiolefin.

The preparation of butyl rubber is described in U.S. Pat. No. 2,356,128,which is incorporated herein by reference. Butyl rubber generally has anumber average molecular weight of about 5,000 to about 500,000,preferably 80,000 to 250,000 and a Wijs Iodine No. of about 0.5 to 50preferably 1 to 15. Low molecular weight butyl rubber is generallydefined as having a M_(v) of 5,000 to 30,000 and 2-10 mole %unsaturation. The viscosity average molecular weight (M_(v)) ofcommercial butyl rubber is about 100,000 to about 500,000, preferablyabout 250,000 to 500,000.

The polymer backbone of commercial butyl rubber is made up primarily ofisobutylene units, with just a few percent isoprene units. The isopreneunits contribute the small amount of unsaturation present in butylrubber. The basic preparative equations are represented by: ##STR1##which combine to form its main structure: ##STR2## wherein n+1represents the number of isoolefin units incorporated in the butylrubber, while m represents the number of diolefin units present,substantially as isolated units. The conjugated diolefin loses its dieneunsaturation upon its incorporation into the polymer backbone.

Thus butyl rubber, as presently produced, contains only a smallpercentage of unsaturation, in the form of the monoolefin structureassociated with the isoprene residue which is incorporated more or lessrandomly throughout the polymer chain.

The reactivity of the butyl rubbers and consequently their cure rate issubstantially less than the high unsaturation natural and syntheticrubbers. In an effort to improve cure characteristics of the butylrubbers, these synthetic polymers have been halogenated. Halogenatedbutyl rubber has contributed significantly to the elastomer industry. Amethod of preparing halogenated butyl rubber is described in U.S. Pat.No. 3,099,644 which is incorporated herein by reference. Bothchlorinated and brominated butyl rubbers are known in the art. Thestructural formula for halogenated butyl rubber is typically representedas being: ##STR3## where X represents the halogen and n, l and m havethe same values as described above for butyl rubber. This structure,however, is one of several which can be formed, depending on theconditions of halogenation, the halogenating agent, used etc. Otherstructural configurations which may occur in halogenated butyl rubbersare ##STR4## It will be noted that in each case the halogen is presentas a secondary or tertiary allylic halogen.

More recently, U.S. Pat. No. 4,288,575 to Irwin Gardner (which has aneffective filing date of Mar. 7, 1977) discloses a new structuralconfiguration for the halogenated rubber where the rubber containsconjugated diene whih is represented as ##STR5##

In this structure the halogen, X, is in a primary allylic position. Themethod disclosed in U.S. Pat. No. 4,288,575 for preparing these rubbersinvolves the use of a copper oxide catalyst useful fordehydrohalogenation of butyl rubber to form a conjugated diene rubber.

As shown in Example 6 of the Gardner patent U.S. Pat. No. 4,288,575 thisprimary halogen is in a more stable configuration than the secondaryhalogens of the prior art and is not readily removed. The copper oxidecatalyst was taught in Gardner's earlier U.S. Pat. No. 4,145,492 to be adehydrohalogenation catalyst suitable for the preparation of conjugateddiene rubber. Where Gardner produces polymers containing the structureof Formula V that structure is invariably associated with conjugateddiene.

Table I of U.S. Pat. No. 4,288,575 shows various halogenated conjugateddiene-containing polymers which are shown to have the halogen in theprimary position. Not surprisingly, the residual halogen is alwaysassociated with substantial amounts of conjugated diene. Since thecatalyst is a dehydrohalogenation catalyst, dehydrohalogenation isproportional to the degree of contact of polymer with the catalyst, andsimilarly, the degree of rearrangement of halogen from the secondary tothe primary position is related to the degree of dehydrohalogenation.

Where high amounts of residual halogen are present in the polymer, as inRun A of Table I of U.S. Pat. No. 4,288,575, it is the result of aninitially high level of halogenation; here 1.95 wt. % bromine. Since thedegree of rearrangement is proportional to the degree ofdehydrohalogenation Gardner's polymers cannot be low in conjugated dieneand at the same time have appreciable amounts of halogen present in theprimary allylic position.

In 1979 Van Tongerloo et. al. disclosed a brominated butyl rubber whichwas low in conjugated diene content (if any) and had the primary halogenconfiguration. The polymer is represented as having the structure##STR6## The reference states that the polymer was produced by aproprietary method and Van Tongerloo et. al. disclose only thatrearrangement to the more stable primary configuration can beaccomplished in brominated butyl rubber "under a variety ofconditions--for example, in the presence of acid, free radicals, basesor heat." See Van Tongerloo, A. and Vukov, R., Proceedings,International Rubber Conference, Milan, Italy, 1979, p. 70ff. Theskilled chemist will recognize that this gratuitous disclosurerepresents the techniques which can be enumerated to accomplish aninfinite number of reactions. The disclosure in no way teaches anymethod to prepare the polymer disclosed.

Van Tongerloo et. al. designate the methylene configuration of FormulaVI above as "EXO" and the primary bromo configuration of Formula V as"ENDO". It is alleged that even at ratios of ENDO:EXO of 71:16 there isno clear indication of a correlation between vulcanizate properties andpolymer microstructure. Hence, Van Tongerloo et. al. have notappreciated that the polymer which they purportedly made by anundisclosed proprietary process has any properties which are differentthan those of conventional halogenated butyl rubber.

Subsequent to the making of the instant invention, Vukov disclosed thatcertain model compounds can be heated to 150° C. for 30 minutes toaccomplish a molecular rearrangement as follows: ##STR7## No substantialrearrangement of the chlorinated model was observed. See Vukov, R.,"Halogenation of Butyl Rubber and The Zinc Oxide Cross-Linking Chemistryof Halogenated Derivatives" which was presented to the ACS RubberDivision on Oct. 25, 1983. Those skilled in the art will recognize thatwhat is true about simple molecules (model compounds) may notnecessarily be true about complex polymer molecules.

SUMMARY OF THE INVENTION

It has surprisingly been found that halogenated butyl rubbers, low inconjugated diene, having a substantial portion of their halogen in aprimary configuration can be prepared by the rearrangement of thestructure of conventional chlorinated and brominated butyl rubber.

These unique polymers surprisingly exhibit more rapid cure rates andbetter vulcanized adhesion to high unsaturated rubbers than can beachieved with conventional brominated butyl rubber. Surprisingly, thechlorinated butyl rubbers of this invention exhibit a faster cure ratethan conventional brominated butyl rubbers.

DETAILED DESCRIPTION

This invention relates to halogenated butyl rubber having improved cureand adhesion properties. More particularly, it relates to halogenatedbutyl rubber wherever a significant fraction of the available halogen ispresent as a primary allylic halogen.

In the practice of this invention a conventional halogenated butylrubber, prepared using commercially known techniques is treated to causean isomeric rearrangement of the halogen from the secondary allylicconfiguration to a primary allylic configuration. The isoprene utilizedin the manufacture of butyl rubber is generally incorporated into therubber in the following configuration: ##STR8## the halogen is generallyincorporated in a configuration depicted as ##STR9## wherein X ishalogen. The site of unsaturation is external to the backbone of thepolymer. In the butyl rubber polymers of this invention the halogen isincorporated in a structure having the configuration ##STR10## Otherhalogen configurations include ##STR11## Throughout the specificationand claims the configurations of formulas VIII, IX and X will bereferred to as Type I, II and III configuration respectively.

The polymers of this invention are distinguished from the polymers ofU.S. Pat. No. 4,288,575 in that they contain less than 0.25 mole %conjugated diene and at least 0.6 wt. % halogen, wherein at least 20mole % to 100 mole % of the halogen is in the Type III configuration.Generally, about 25 mole % to about 90 mole percent of the halogen willbe present in the Type III configuration. Preferably, at least 30 mole %to about 85 mole %, more preferably at least 40 mole % of the halogen ispresent as the Type III configuration. The halogenated butyl rubber maybe either chlorinated or brominated. The halogen content is preferablyat least 0.8 wt. % to about 2.4 wt. %, more preferably the halogenatedbutyl rubber contains at least 0.9 wt. % halogen to about 1.8 wt. %,e.g. about 1.4 wt. %.

In the process of preparing the halogenated butyl rubber of thisinvention some halogen may be lost as a result of some degree ofdehydrohalogenation which may result in the formation of a conjugateddiene structure. The conjugated diene (CD) content of the polymer,however, will be less than 0.25 mole %. Generally, the CD content willbe less than 0.20 mole % preferably less than 0.15 mole %.

In the preparation of the halogenated butyl rubber of this invention thehalogenated rubber is prepared by treating conventional halogented butylrubber with a Friedel-Crafts catalyst, e.g. ZnCl₂. The brominated formis prepared by treating conventional brominated butyl rubber with HBr.

In the Friedel-Crafts catalytic isomerization of halogenated butylrubber the halogenated butyl rubber is dissolved in a nonpolar solventand contacted with a Friedel-Crafts catalyst. Preferably, the reactioncan be carried out in the presence of anhydrous HCl or anhydrous HBr,preferably selecting the same halogen for the acid as is present in thecatalyst.

Any hydrocarbon which is a solvent of butyl rubber can be used as thenonpolar solvent. Illustrative non-limiting examples of such solventsare hexane, heptane, octane, toluene, xylene etc. Since butyl rubber isgenerally halogenated in a solution of hexane, hexane is the preferredsolvent. The concentration of halogenated butyl rubber in solvent is notcritical. However, the concentration must not be so small as to make theprocess uneconomical or so large that the polymer cement is too viscousto handle. Generally, the polymer concentration in the solvent is about5 wt. % to about 25 wt. %, preferably about 10 wt. % to about 15 wt. %.

The Friedel-Crafts catalyst can be added directly to the polymersolution or it can first be dissolved in diethyl ether. Dissolving thecatalyst in ether results in a fine dispersion of catalyst upon additionto the hexane cement. Preferably, in selecting a halogenated catalystthe halogen of the catalyst corresponds to the halogen of the polymer.

Suitable Friedel-Crafts catalysts include ZnCl₂, FeCl₃, BF₃, BCl₃,aluminum alkyl halides and trialkyl aluminum of the formulas R₃ Al, R₂AlX and RAlX₂ wherein R is an alkyl group of 1 to 8 carbon atoms,preferably C₁ -C₂ alkyl, and X is halogen preferably chlorine orbromine; gallium chloride, zinc bromide, aluminum chloride, aluminumbromide, and antimony halides. The ratio of catalyst to rubber on aweight basis can be about 1:100 to about 1:1000, preferably about 1:200to about 1:300.

The reaction temperature can vary from about 20° C. to 150° C.,preferably about 40° C. to about 130° C., more preferably about 60° C.to about 110° C., e.g. 90° C. The reaction time can be about 2 minutesto about 3 hrs. Longer reaction times may be used since therearrangement results in stable polymer. Preferably, the reaction timeis about 5 minutes to about 60 minutes.

The quantity of anhydrous HCl or HBr, when used, is not critical.However, it is preferably present in excess with respect to theFriedel-Crafts catalyst. The ratio of HCl or HBr to catalyst can beabout 0.5/1 to 100/1, preferably about 5/1 to 20/1, most preferablyabout 10/1. In a preferred method the HCl or HBr is added by purging thereaction mixture with a stream of anhydrous HCl or HBr continuouslythroughout the reaction.

The method of this invention for the isomerization of conventionalchlorinated butyl rubber to the primary allylic chlorine containingpolymer of this invention is illustrated by the following examples:

EXAMPLE I

A commercial chlorinated butyl rubber was dissolved in heptane so that a15% by weight solution of rubber (928 grams) was prepared. ZnCl₂ wasdissolved in ether (3.1 grams in 25 ml) and added with constant stirringto the chlorinated butyl rubber cement which had been heated to 84° C.The mixture was purged with a continuous gas stream of anhydrous HCl ata rate of about 11.5 cc/min. The weight ratio of HCl to ZnCl₂ was about10/1. The results are tabulated in Table I.

                  TABLE I                                                         ______________________________________                                        Chlo-     Moo-                                                                rine      ney             Isomer        CD                                    content   ML              Type (1)      (2)                                   Time  (wt.    (1+8)                        IV   con-                          (min) %)      125° C.                                                                        Mv    I    II   III  (3)  tent                          ______________________________________                                         0    1.35    40      433 K 0.19 0.71 0.   0.10 0.03                          105   1.07    16      300 K 0.07 0.38 0.48 0.07 0.13                          ______________________________________                                         (1) mole fraction                                                             (2) mole percent                                                              (3) Type IV is                                                                ##STR12##                                                                

It is evident that the process of this invention produces a chlorinatedbutyl rubber isomer having a significant fraction of the chlorinepresent in the type III configuration and with substantially noconjugated diene.

EXAMPLE II

The method of Example I was repeated with minor modifications. The ZnCl₂was added directly to the polymer cement without first dissolving it inether. The reaction time was 135 minutes. It was found that the ZnCl₂was wet; therefore 4 grams of FeCl₃ was added and reacted for anadditional 35 minutes. The product had a chlorine content of 1.09 wt%(as determined by X-ray analysis), a Mooney viscosity of 22.1[ML(1+8)125° C.], a CD content of 0.05 mole % and a Mv of 415,000. Theratio of Type I, II, III and IV configuration as found by 400 MHz NMRwas 0.12:0.55:0.22:0.11.

EXAMPLE III

Example I was repeated using 528 grams of chlorinated butyl rubber inheptane (15 wt% solution). Four grams of fresh ZnCl₂ was added and theisomerization was carried out for about 66 minutes at 90° C. Theanhydrous HCl flow rate was about 15 cc/min. The system was then cooledto 0° C. and 8 g Cl₂ was added through a glass frit in order to furtherhalogenate the polymer. The final prooduct had a chlorine content of1.42 wt%, a Mooney of 16.5, an Mv of 290,000 and a residual zinc contentof 60 ppm. The number average molecular weight was 114,000. Based on 400MHz NMR the ratio of types I, II, III and IV configuration was0.0:0.66:0.26:0.08.

EXAMPLE IV

The polymers of Examples I, II and III were tested in zinc oxide curesagainst commercial chlorinated and brominated butyl rubber. The resultsare shown in Tables II and III.

                  TABLE II                                                        ______________________________________                                                       A     B       C       D                                        ______________________________________                                        Component.sup.(a)                                                             E-I.sup.(1)      100     --      --    --                                     E-2.sup.(2)      --      100     --    --                                     E-3.sup.(3)      --      --      100   --                                     R-I.sup.(4)      --      --      --    100                                    Stearic Acid     1.0     1.0     1.0   1.0                                    IRB #5.sup.(5)   40      40      40    40                                     ZnO(NBS)         5       5       5     5                                      Monsanto Rheometer Results                                                    (ASTM 2084)                                                                   M.sub.H, in-lbs  42.2    40.3    50    39                                     M.sub.H -M.sub.L, in-lbs                                                                       25.6    26.3    35    24.2                                   t 50, min        8.2     7.0     6.1   7.5                                    t 90, min        23.0    20      20    15                                     t s2, min        1.7     1.5     1.2   2.95                                   Slope,           2.36    2.53    3.53  2.37                                   in-lb/min.                                                                    Mooney Scorch    7.2     6.8     5.6   21.                                    5 pts @ 125° C. (min)                                                  ______________________________________                                         .sup.(a) Amounts shown are parts by weight                                    .sup.(1) Chlorinated butyl rubber of Example I                                .sup.(2) Chlorinated butyl rubber of Example II                               .sup.(3) Chiorinated butyl rubber of Example III                              .sup.(4) Chlorinated butyl rubber used in Example I-III to make polymer o     this invention with a chlorine content of 1.35                                .sup.(5) HAF black  oven dried                                           

A comparison of the cure response shows that, notwithstanding the factthat polymer of Examples I and II had a chlorine content 20% lower thanthe control (Run D), the state of cure (M_(H) -M_(L)) was at least ashigh and the rate of cure (slope) was at least as fast. Additionally theshorter scorch times also indicate a faster onset of cure. Where thepolymer of this invention (Run C) had a chlorine content equivalent tothe control (Run D), the state of cure was even greater notwithstandingthe fact that the type III content of the polymer was about 26%.

                  TABLE III                                                       ______________________________________                                                       E     F       G       H                                        ______________________________________                                        Component                                                                     E-III            100     --      100   --                                     R-II.sup.(1)     --      100     --    --                                     Commercial       --      --      --    100                                    Chlorinated                                                                   Butyl                                                                         Stearic Acid     1.0     1.0     1.0   1.0                                    IRB #4.sup.(2)   50      50      50    50                                     ZnO (NBS)        5       5       --    --                                     Calcium          --      --      1.5   1.5.sup.(3)                            Stearate                                                                      Monsanto Rheometer Results                                                    M.sub.H          81      64      73.5  59.5                                   M.sub.H -M.sub.L 61      39.1    56.8  41.3                                   t.sub.50         14.2    12.4    13.1  15.8                                   t.sub.90         37.5    17.2    30    25.5                                   t.sub.s2         0.75    4.5     3.5   3.8                                    Slope            2.95    4.37    4.47  1.86                                   Mooney Scorch                                                                 3 pts @ 135° C.,                                                                        3.4     11.6    6.4   --                                     (min.)                                                                        5 pts @ 125° C.,                                                                        --      --      --    21                                     (min.)                                                                        ______________________________________                                         .sup.(1) Brominated polymer 1.85 wt % bromine, M.sub.v = 490,000              .sup.(2) SRF furnace black                                                    .sup.(3) Present in polymer following commercial production.             

The surprising finding here is that the chlorinated polymer (26% typeIII) of this invention has a faster cure than a brominated polymerhaving a bromine content of 1.85 wt%. (Compare E and F).

Cure response of the isomerized halobutyl rubber, E-III, was furthermodified by addition of 1.5 parts of calcium stearate (Composition G) todelay cure initiation (scorch time, t_(s2)). In comparison to thereference polymer (R-II) it still shows a significantly higher state ofcure, faster initial cure rate (slope) and shorter cure initiation time.Compared to a commercially produced chlorinated butyl rubber samplecontaining 1.35 wt. % chlorine and calcium stearate, the isomerizedhalobutyl had a higher state of cure and significantly faster initialcure rate (slope).

EXAMPLE V

Example I was repeated using 200 grams of a 25% solution of chlorinatedbutyl rubber. Instead of ZnCl₂, the catalyst used was 0.327 g of FeCl₃in 66 g of CHCl₃. The reaction was carried out at 50° C. and the resultsare shown in Table IV.

                  TABLE IV                                                        ______________________________________                                        Run   Cl       Configuration Type                                                                             Mv ×                                    Time  wt %     I        II    III   10.sup.-3                                                                            gel                                ______________________________________                                        20    1.06     0        .29   .71   359    12.4                               60    1.05                          708                                       105   --                            gel                                       ______________________________________                                    

It is apparent that ferric chloride is a more active catalyst andshorter reaction times can be used to achieve a high degree ofisomerization.

EXAMPLE VI

H₂ SO₄ was used in an attempt to isomerize brominated butyl rubber.Concentrated H₂ SO₄ (16 g) was added to 300 grams of rubber in 2700grams of solvent (Isopar G, an isooctane process by-product). Thereaction was run at 80° C. The bromine content was reduced from 1.85 wt%to 1.4 wt%. The viscosity average molecular weight of the rubber wasreduced to 17,000 from an original value of 492,000. While significantisomerization occurred, the gross degradation of molecular weightresulted in a product which has value only as a low molecular weightbrominated butyl rubber. In applications requiring high molecular weightsuch a material would not be useful.

EXAMPLE VII

Approximately 290 grams of a 20% solution of brominated butyl rubber washeated with HBr at 30° C. About 110 cc/min of HBr was bubbled throughthe solution and samples removed periodically for analyses. The resultsare shown in Table V.

                  TABLE V                                                         ______________________________________                                        Time   Br         --Mv ×                                                                          Configuration                                       (Sec)  wt %       10.sup.-3                                                                             I:      II:  III                                    ______________________________________                                          0    2.06       433     .15     .81  .04                                     417   --         417     --      --   --                                      775   2.32       231     --      --   --                                     2430   2.58       210     .04     .325 .634                                   3626              210      .048   .270 .714                                   ______________________________________                                    

While there was substantial rearrangement, there was also severedegradation of the polymer. Attempts to cause rearrangement ofchlorinated butyl rubber using HCl were unsuccessful.

EXAMPLE VIII

The experiment of Example VII was repeated over a temperature range of-52° to -42° C. After 397 seconds of treatment with anhydrous HBr thebromine content increased from 1.87% to 2.13 wt% while the Mv which wasinitially 492,000, dropped to 370,000. The ratio of Type I, II, III andIV configuration was 0.1:0.17:0.56:0.17 as compared to original valuesof 0.162:0.764:0.074:0. Hence, the low temperature treatment ofbrominated butyl with HBr results in substantial rearrangement with anacceptable degree of degradation of the polymer.

It is apparent from the foregoing examples that it is insufficientmerely to select an acid to accomplish the isomerization of thisinvention. The appropriate acid must be selected and it must be utilizedat the proper temperature. Otherwise, severe degradation of the basepolymer i.e. reduction in molecular weight, occurs.

The viscosity average molecular weight of the product of this inventionshould be at least 100,000, preferably at least 200,000, most preferablyat least 250,000; e.g. at least 300,000.

In conducting the isomerization process of this invention to produce abrominated butyl rubber having a significant fraction of the bromine inthe primary allylic configuration the reaction temperature should beless than 40° C., preferably less than 30° C., more preferably less than10° C.; e.g. less than 0° C. In a particularly preferred embodiment subzero reaction temperatures in the order of -10° C. to about -100° C. maybe advantageously used; preferably the sub zero temperatures utilized incarrying out the process of this invention is about -30° to about -75°C. The reaction time may vary from about 2 minutes to about 3 hours,preferably from about 5 minutes to about 60 minutes.

The isomerization of the brominated butyl rubber is carried out insolution using a non-polar hydrocarbon solvent. The solvents suitablefor the chlorinated butyl rubber isomerization reaction may be used forbrominated butyl rubber also. The concentration of polymer in thesolvent is preferably about 5% to about 25% by weight as in thechlorinated polymer, and the preferred polymer concentration is about10% to 20%.

The HBr is preferably anhydrous, and an excess of acid relative topolymer is required. The mole ratio of acid to brominated polymer shouldbe about 0.5/1 to 50/1, preferably about 6/1 to about 12/1, e.g. about10/1.

The modified cure response observed with halogenated butyl rubbershaving a significant amount of halogen in the primary allylicconfiguration suggests that they may covulcanize with other rubbers andhave improved adhesion. This is demonstrated by the following examples.

EXAMPLE IX

A commercial sample of brominated butyl rubber produced in a solutionprocess (SOL Br-Bu) was compared with an isomerized brominated butylrubber of this invention in a zinc oxide cure system as described below.

    ______________________________________                                                               Isomerized                                                           SOL Br--Bu                                                                             Br--Bu                                                 ______________________________________                                        Br (wt. %)      1.8-2.2    2.0-2.2                                            Ca Stearate (wt. %)                                                                           1-2        2.5                                                ESBO.sup.(1) (wt. %)                                                                          1-2        2                                                  mole % Type III Br                                                                            10         65                                                 CD mole %       --         .001                                               ______________________________________                                         .sup.(1) epoxidized soybean oil.                                         

The ESBO and calcium stearate act as cure retardants. The rubbers werecompounded with 50 parts of SRF black, 5 parts zinc oxide and 1 part ofstearic acid to 100 parts by weight of rubber. The compounds were testedon the Monsanto Rheometer at 160° C. for 30 minutes using a 5° arc. Theresults were as follows:

    ______________________________________                                                              Isomerized                                                           SOL Br--Bu                                                                             Br--Bu                                                  ______________________________________                                        M.sub.H -M.sub.L (in-lb)                                                                     22         20-27                                               t.sub.90 (minutes)                                                                           11         4-5                                                 ______________________________________                                    

Notwithstanding the fact that the experimental rubber contained higherlevels of cure retardant it cured faster than the conventionalbrominated butyl rubber.

EXAMPLE X

The rubbers of Example IX were compared for adhesion properties bypreparing innerliner formulations and curing them to a tire carcasscomposition using the formulations shown in Table VI, all values beingparts by weight:

                  TABLE VI                                                        ______________________________________                                                   INNERLINER                                                                                            Isomerized                                 Component    CARCASS   SOL Br--Bu  Br--Bu                                     ______________________________________                                        Natural Rubber                                                                             100       --          --                                         SOL Rubber   --        100         --                                         Isomerized Rubber                                                                          --        --          100                                        N-660 Black  50        55          55                                         Flexon 641.sup.(1)                                                                         --        6           6                                          Sundex 790 DOP                                                                             5         --          --                                         Escorez 1102.sup.(2)                                                                       2         6           6                                          Stearic Acid 2         2           2                                          ZnO          5         3           3                                          Sulfur       2.3       0.5         0.5                                        MBTS         --        1.5         1.5                                        Santocure NS.sup.(3)                                                                       1         --          --                                         Maglite K.sup.(4)                                                                          --        0.25        0.25                                       Wingstay 100.sup.(5)                                                                       2         --          --                                         Struktol 40 MS.sup.(6)                                                                     --        7           7                                          ______________________________________                                         .sup.(1) Naphthenic rubber process oil  Exxon Chem. Co.                       .sup.(2) Hydrocarbon tacifier resin  Exxon Chem. Co.                          .sup.(3) Cure accelerator, N--tbutyl-2-benzothiazole sulfenamide  Monsant     Co.                                                                           .sup.(4) MgO  Merck Co.                                                       .sup.(5) Antioxidant, mixed diarylp-phenylene-diamines-Goodyear Chemicals     .sup.(6) Proprietary mixed resin  Struktol Co.                           

The carcass composition and innerliner compositions were laminated andvulcanized together using 2,000 psi at a temperature of 150° C. for 30minutes. The results are shown in Table VII.

                  TABLE VII                                                       ______________________________________                                        COMPARISON OF BROMINATION BUTYL RUBBERS                                       IN INNERLINER TEST                                                                                   Isomerized                                                            SOL Br Bu                                                                             Br                                                     ______________________________________                                        Scorch, T3, 135° C.;                                                                    25        15                                                 min.                                                                          Adhesion to NR                                                                carcass, lb./in.                                                              @ 25° C.  110       180                                                @ 100° C. 39        55                                                 ______________________________________                                    

The rheometer and stress-strain properties of the halogenated polymersin these compositions were similar. However, it is evident from theabove results that the halogenated butyl rubbers of this invention aresuperior in adhesion to conventional rubbers. Hence, they would findparticular utility in applications requiring good adhesion performance,e.g., tubeless tire innerliners.

We claim:
 1. A method for improving the adhesion of a halogenated butylrubber composition to a tire carcass which comprises incorporating intosaid composition as the halogenated butyl rubber, an improvedhalogenated butyl rubber having a conjugated diene unsaturation contentof less than 0.25 mole %, a halogen content of at least 0.6 wt. %, andat least 20 mole % of the halogen being in a primary allylicconfiguration.
 2. The improved method according to claim 1 wherein thehalogen is chlorine.
 3. The improved method according to claim 1 whereinthe halogen is bromine.
 4. The improved method according to claim 1wherein the halogen content is about 0.8 wt. % to about 2.4 wt. %. 5.The improved method according to claim 1 wherein the halogen content isat least 0.9 wt. %.
 6. The improved method according to claim 1 whereinat least 25 mole % of the halogen is present in the primary allylicconfiguration.
 7. The improved method according to claim 6 wherein about25 mole % to about 90 mole % of the halogen is present in the primaryallylic configuration.
 8. The improved method according to claim 1wherein said composition comprises an innerliner composition.